UV curable coating for golf balls

ABSTRACT

An UV curable coating for a golf ball or a similar game ball that the UV curable coating is the reaction product of at least one UV-reactive component, a polyfunctional aziridines, and a photo-initiator. The UV curable coating is substantially free of solvent, therefore, contains nearly 100% solids.

FIELD OF THE INVENTION

[0001] The present invention relates to an ultraviolet (UV) curablecoating. In particular, though not exclusively, the present inventionrelates to a high solids UV curable coating useful in a golf ballapplication.

BACKGROUND OF THE INVENTION

[0002] Golf balls can be classified as one-piece, two-piece, andthree-piece balls. One-piece balls are molded from a homogeneous mass ofmaterial with a dimple pattern molded therein. Two-piece balls arecomprised of a cover molded over a solid core. The core of a two-pieceball is typically formed of rubber and can be solid, semi-solid or havea liquid center. Three-piece balls, traditionally, include a rubberinner core, elastic wrappings and a balata or SURLYN® ionomer cover. Themore recent trend in the golf ball art is towards the development ofmulti-component golf balls such as balls having two or more coverlayers, two or more core layers or both multiple core and multiple coverlayers.

[0003] Golf ball covers are presently formed from a variety ofmaterials, such as balata, SURLYN® ionomer resin, IOTEK® resin andpolyurethane, depending upon the performance characteristics desired forthe golf ball. One of the softest materials conventionally used to formgolf ball covers is balata, which is the trans form of the 1,4-chainpolymer of isoprene. For many years, balata was the standard cover stockmaterial used in forming most golf balls. Balata covered balls arefavored among professionals and more advanced amateur players becausethe softness of the cover allows the player to achieve spin ratessufficient to precisely control ball direction and distance,particularly on shorter approach shots.

[0004] However, because of its softness, balata is susceptible to cutsor other damage to the cover resulting from a “mis-hit” shot.Accordingly, harder, more durable cover materials, e.g., SURLYN® ionomerresin, have been developed which provide higher durability, but lessspin and feel, than the balata balls. SURLYN® resins are generally ioniccopolymers of an olefin such as ethylene and a metal salt of anunsaturated carboxylic acid such as acrylic acid, methacrylic acid ormaleic acid. Metal ions, such as lithium, zinc or sodium are used toneutralize some portion of the acidic groups in the copolymer resultingin a thermoplastic elastomer for use as a golf ball cover.

[0005] Additionally, various softening comonomers such as n-butylacrylate may be added during the ionomer manufacturing process toimprove golf ball performance characteristics such as spin and feel. Inthe early 1980s, low modulus SURLYN® resin were introduced andsubsequently utilized to impart more spin and an improved, balata-likefeel to golf balls.

[0006] Primer coat and topcoat layers are commonly applied to the golfball cover to provide a high gloss and an overall enhanced appearance tothe ball. Solvent-borne coatings are currently used as topcoats for golfballs or similar game balls. These coatings provide good adhesion to thesurface of the balls, and good abrasion resistance. However, the solventtype systems have serious environmental pollution problems, and thedisadvantage of long cure times, or high curing temperatures. U.S. Pat.No. 4,871,589 (hereinafter '589 patent) discloses a method of treatinggolf balls by applying solvent-borne coating onto a thermoplasticionomer covered golf ball. The solvent-borne coating of '589 patentcontains 50% solvents and needs to be cured for 10 minutes at 50° C.

[0007] In light of the increasing regulation of volatile organiccompounds (VOC), the use of traditional solvent-borne adhesive isbecoming problematic. To eliminate the problems posed by solvents,water-borne replacements have been developed. Current water-bornecoatings suffer from drawback of long curing time. U.S. Pat. No.4,459,326 discloses a water-based composition for coating syntheticplastic surfaces. The water-based coating need to dry for ½ to 4 hours.

[0008] U.S. Pat. No 4,278,578 (hereinafter '578 patent) teaches anaqueous coating containing polyfunctional aziridines. The '578 patentindicates that the use of more than 3% aziridine is not beneficial tocoating properties.

[0009] U.S. Pat. No. 5,300,325 discloses a use of an aziridine in awater-borne primer to promote adhesion between the solvent-borne topcoatand the cover of a golf ball. The primer and topcoat are co-cured andcrosslinked at 54° C. for six hours.

[0010] U.S. Pat. No. 6,146,288 discloses a UV-curable coating and methodfor coating golf balls and other substrates with a material thatincludes one or more low viscosity polyether acrylates, a functionalcarbodiimide resin, one or more low viscosity aliphatic urethanepolyacrylate oligomer, and a photoinitiator selected from one or more ofS mono-aryl ketones, trimethylbenzoyldiphenyl phosphinates, and/orphosphine oxides. In addition, a method of curing a UV-curable coatingis disclosed. The method includes the steps of spraying the formulationonto the exterior of a substrate, surrounding the substrate in an inertgas environment, and irradiating the substrate with ultravioletradiation from a doped medium pressure mercury vapor lamp.

[0011] SURLYN® resin is the most widely used material to make golf ballcover layers. SURLYN® resin is an ionomer from the copolymer of ethyleneand methacrylic acid. It is difficult for an UV curable coating toadhere to SURLYN® surface, in part because of the high shrinkage duringthe polymerization process. Urethane cured coatings are not easilyadhered to ionomers. The present invention resulted from solving anadhesion problem of a UV curable coating which can be effectivelyutilized in coating ionomer substrates.

[0012] The problem addressed by the present invention was to provide anUV curable coating which would be capable of developing excellentadhesion, even on substrates which are traditionally difficult to adhereto with a UV coating. In addition, the UV curable coating of the presentinvention provides a high gloss finish, does not require the golf ballto be surrounded by an inert gas, is low in yellowing, and also offersgood stain resistance and durability.

SUMMARY OF THE INVENTION

[0013] The present invention relates to an UV curable coating comprising(a) at least one UV-reactive component, (b) a polyfunctional aziridine,and (c) a photo-initiator. The UV curable coating of this invention issubstantially free of solvents, and therefore, provides a nearly 100%solid system. The UV curable coating of the present invention isparticularly suitable for coating ionomer substrates. Unexpectedly, theUV curable coating of the invention shows improved whiteness index (WI)compared to typical UV coatings. Specifically, the present inventiondiscloses a high solids UV curable coating for golf balls or a similargame ball application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The UV curable coating of this invention comprises the reactionproduct of (a) at least one UV-reactive component, (b) a polyfunctionalaziridines, and (c) a photo-initiator.

[0015] Polyfunctional aziridines (“polyaziridine”) suitable for thepurposes of the present invention correspond to the formula:

R—[X—N(CH₂)₂]_(m)

[0016] in which R is an organic aliphatic radical or a hydrogen atom, Xis an alkylene group which may contain an ester group, an ether group,an amide group or a similar inert group, and m is a number of 2 to 4.

[0017] Preferred polyaziridines are those in which

X=—(CH₂)_(n)—O—CO—(CH₂)₁—

[0018] where n=1 to 3, 1=1 to 3, and m=3 and R is a CH.sub.3—CH.sub.2—Cradical.

[0019] Another preferred polyfunctional aziridines are those in which

X=—(CH₂)_(n)—O—CO—(CH₂)₁—

[0020] where n=1, 1=2, and m=3 and R is an OH —CH.₂—C radical.

[0021] The polyfunctional aziridine useful herein is preferably tri- ormore highly functional compounds. The preferred materials include:pentaerythritol-tris-(beta-(N-aziridinyl)propionate);trimethylol-propane-tris-(.beta.-(N-aziridinyl)propionate); and mixturesthereof. Ethylenimine Technologies (EIT) sell representativepolyfunctional aziridines under the trade name XAMA®-7 and XAMA®-2,which are particularly preferred in the present invention.

[0022] The polyfunctional aziridine is typically utilized in an amountof at least 0.1% by weight percent of the UV curable coating in thepresent invention. The polyfunctional aziridine is preferably utilizedin an amount from about 0.1% to 15%, with 0.5% to 8% speciallypreferred, by weight percent of the UV curable coating in the presentinvention. The polyfunctional aziridine contributes to the adhesion ofthe UV curable coating to the golf ball cover. However, the use of ahigh amount of polyfunctional aziridine might cause the UV coating toundergo yellowing after cure. Surface treatments, such as vibratoryabrasion and corona or plasma treatment, or other methods that result insurface modifications to the golf ball cover, may be used to enhanceadhesion of the topcoat to the golf ball cover.

[0023] One of the UV reactive components in the present invention is anUV curable oligomer. Proper selection of the oligomer is important toobtaining the desired physical properties of the resulting coating. Thesuitable UV curable oligomers in the present invention are thoseoligomers containing acrylate functionality, namely an acrylate doublebond. The double bond can open to form a crosslinked polymer networkwhen irradiated with UV light in the presence of photo-initiators. Thesuitable UV reactive components in the present invention includeurethane acrylate, epoxy acrylate, polyether acrylate or polyesteracrylate, and are known in the art. However the polyether and polyesteracrylates must be low in acid content, such as an acid number of lessthan 10, preferably less than 5, to avoid premature reaction with thepolyaziridine component. In general, urethane acrylate oligomers imparttoughness and abrasion resistance to the final coatings, while epoxyacrylate oligomers and polyester acrylate oligomers impart hardness andchemical resistance. The UV curable acrylate component will consist ofbetween 30 to 80 weight percentage of the total composition weight ofthe UV-curable coating. The polyether acrylates advantageously have alow viscosity, preferably in the range of about 75 to about 250centipoise. Examples of commercially available oligoether acrylatesinclude LR 8967, and 8863, which are all available from BASF.

[0024] The preferred UV curable component of the invention is urethaneacrylate oligomers formed by the reaction of an isocyanate group, and anacrylic monomer having at least one hydroxyl group. Preferred acrylicmonomers include hydroxyethyl acrylate, hydroxypropyl acrylate andcaprolactone acrylate. Suitable isocyanates include aliphaticisocyanates, cycloaliphatic isocyanates, alkaryl isocyanates, arylalkylheterocyclic isocyanates and aryl isocyanates. Suitable isocyanates ofthe invention could be monoisocyanates, diisocyanates, ortriisocyanates. The diisocyanates are the preferred isocyanates of theinvention.

[0025] Examples of diisocyanates include tetramethylenediisocyanate,pentamethylene diisocyanate, octomethylene diisocyanate,dodecylmethylenediisocyanate, 3,3-diisocyanatodipropyl ether, xylylenediisocyanate, meta-phenylenediisocyanate,1-methylphenylene-2,4-diisocyanate, 2,6-toluenediisocyanate, 2,6-toluenediisocyanate,cyclohexane-1,4-diisocyanate,methane-bis(cyclohexy-4-isocyanate), andisophorone diisocyanate.

[0026] Preferred diisocyanates include Tolylene diisocyanate (TDI),Hexamethylene diisocyanates (HDI), ), Norbornane diisocyanates (NBDI),Isophorone diisocyanates (IPDI), Diphenylmethane diisocyanates (MDI),bis(4-isocyanatocyclohexyl) methane (Desmodur® W) and Polyisocyanatesfrom HDI (Desmodur® N-100, Desmodur® N-3200, Desmodur® N3300). Aliphaticdiisocyanates are the most preferred diisocyanates of the inventionbecause of their non-yellowing characteristics.

[0027] In one preferred embodiment, urethane acrylate oligomers areformed by reacting an aliphatic diisocyanate with hydroxy monomer instoichiometric proportions and further reacting this with a long chainpolyol to form a flexible urethane acrylate oligomer.

[0028] Oligomers of molecular weight greater than 8000 can produce acoating with too much flexibility, while oligomers of molecular weightbelow 500 produce a coating that has low impact resistance. Preferably,the oligomers used in the present invention have molecular weightsranging from 500 to 8000, with preferred range from 500 to 5000. Theurethane acrylate oligomer should be utilized in an amount ranging fromabout 30% to 80% by weight percent of the total coating, and morepreferably, between 40% to 70% by weight percent of the total coating.

[0029] The urethane polyacrylate oligomer UV curable component has arelatively low viscosity, preferably in the range of about 8,000 toabout 40,000 centipoise. The aliphatic urethane polyacrylate oligomercomponent provides the abrasion resistance and the resiliency of thepolyurethane coating. As illustrative and non-limiting examples, thealiphatic urethane polyacrylate oligomer component are sold by companiessuch as Sartomer Company Inc., or under the BOMAR® designation by BomarSpecialties, Winsted, Conn.

[0030] In the preparation of an UV curable coating, the UV-curableoligomer is typically utilized in combination with a reactive diluentsystem. Broadly, suitable reactive diluent systems comprise at least oneunsaturated addition polymerizable monomer, which is copolymerizablewith the UV-curable oligomer upon exposure to radiation. The reactivediluent can be monofunctional, difunctional or polyfunctional. A singlepolyfunctional diluent can be used; or a combination of one or moremonofunctional reactive diluents, one or more difunctional reactivediluents, and one or more polyfunctional reactive diluents can be used.

[0031] Particularly preferred reactive diluents are unsaturatedaddition-polymerizable monofunctional, difunctional and polyfunctionalacrylic monomers. Acrylate monomers useful as a reactive diluent systemare well known and examples of such monomers include isobornyl acrylate,phenoxyethyl acrylate, isodecyl acrylate, hexyl acrylate, cyclohexylacrylate, 2-ethylhexyl acrylate, octyl acrylate, nonyl acrylate, stearylacrylate, 2-phenoxy acrylate, 2-methoxyethyl acrylate, lactone modifiedesters of acrylic and methacrylic acid, methyl methacrylate, butylacrylate, isobutyl acrylate, methacrylamide, allyl acrylate,tetrahydrofuryl acrylate, n-hexyl methacrylate, 2-(2-ethoxyethoxy)ethylacrylate, n-lauryl acrylate, 2-phenoxyethyl acrylate, glycidylmethacrylate, glycidyl acrylate, acrylated methylolmelamine,2-(N,N-diethylamino)-ethyl acrylate, neopentyl glycol diacrylate,alkoxylated neopentyl glycol diacrylate, ethylene glycol diacrylate,hexylene glycol diacrylate, diethylene glycol diacrylate, tripropyleneglycol diacrylate, tetraethylene glycol diacrylate, pentaerythritol di-,tri-, tetra-, or penta-acrylate, trimethylolpropane triacrylate,alkoxylated trimethylol-propane triacrylate which contains from 2 to 14moles of either ethylene or propylene oxide, triethylene glycoldiacrylate, tetraethylene glycol diacrylate, polyethylene glycoldiacrylate, 1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate,1,6-hexanediol diacrylate, polyethylene glycol diacrylate, combinationsthereof, and any corresponding methacrylates thereof.

[0032] The reactive diluent system typically comprises from about 10 to60, preferably from about 20 to 50 percent by weight of the total UVcurable coating. The photo-initiator can be any of the knownphoto-initiators. Specific examples include benzophenone, benzoin,acetophenone, benzoin methyl ether, Michler's ketone, benzoin butylether, xanthone, thioxanthone, propiophenone, fluorenone, carbozole,diethyoxyacetophenone, the 2-, 3- and 4- methylacetophenones andmethoxyacetophenones, the 2- and 3-chloroxanthones andchlorothioxanthones, 2-acetyl-4-methylphenyl acetate,2,2′-dimethyoxy-2-phenyl acetophenone, benzaldehyde, fluorene,anthraquinone, triphenylamine, 3- and 4-allyl-acetophenone,p-diacetylbenzene, 3-chloro-2-nonylxanthone, 2-chlorobenzophenone,4-methoxybenzophenone, 2,2′,4,4′-tetrachlorobenzophenone,2-chloro-4′-methylbenzophenone, 4-chloro-4′-methylbenzophenone,3-methylbenzophenone, 4-tert-butyl-benzophenone, isobutyl ether, benzoicacetate, benzil, benzilic acid, amino benzoate, methylene blue,2,2-diethoxyacetophenone, 9,10-phenanthrenequinone, 2-methylanthraquinone, 2-ethyl anthraquinone, 1-tert-butyl-anthraquinone,1,4-naphthoquinone, isopropylthioxanthone, 2-chlorothioxanthone,2-iso-propylthioxanthone, 2methylthioxanthone, 2-decylthioxanthone,2-dodecyl-thioxanthone, 2-methyl- 1-[4-(methylthio)phenyl)]-2-morpholinopropanone-1, combinations thereof and thelike. The photo-initiator or combination of photo-initiators istypically utilized in an amount ranging from about 0.5 to 15, preferablyfrom about 1 to 8 percent by weight of the UV curable coating in thepresent invention. The peak absorbance is typically in the range ofabout 240 nm to about 390 nm.

[0033] In general, exemplary monomers, oligomers, and photoinitiatorscan be found in “Chemistry and Technology of UV and EB Formulations forCoatings, Paints, and Inks”, P. K. T. Oldring, ed., (1991), ISBN 0947798 10.2.

[0034] An UV curable coating, comprising at least one UV reactivecomponent, a polyfunctional aziridine, and a photo-initiator of thepresent invention, may also contain other optional ingredients known tothose skilled in the art of UV curable compositions. An optionalingredient is a whitener that improves the overall appearance of the UVcurable coating. Suitable whiteners include 2,5-Bis (5tert-butyl-2-benzoxazolyl) thiophene (Uvitex® OB from Ciba SpecialtyChemical Co.), 7-(2h-napthol (1,2-d)-triazol-2-yl)-3-phenyl-coumarin(Leucopure® EGM from Clariant).

[0035] Other optional components of the present UV curable coatinginclude surfactants to modify the flow and wetting characteristics ofthe coating

[0036] The UV curable coating as described above of the presentinvention contains more than 90%, preferably greater than 95% solids,more preferably more than 98% solids, and most preferably essentially100% solids. The UV curable outer coating is substantially solvent free(<5%) by weight, preferably less than 2% of volatile organic solvent.Most preferably the coating is essentially solvent-free which avoids theproblems of energy consumption in evaporating the solvent, solventpollution, and the cost of solvent. However, the present UV curablecoating can also be diluted with solvent for improved application tovarious substrates if desired. The choice of solvent employed fordilution is not critical. Preferred solvents are those that areclassified as exempt from (volatile organic component) VOCclassification such as acetone. However VOC containing solvents can alsobe used. For instance, 10% solvent may be incorporated to reduce theviscosity of the UV curable coating in order to carry out the desiredperformance of spraying.

[0037] UV curable coatings can be applied to a substrate to be coated orbonded by various techniques well known in the art e.g. roll coater,curtain coater, vacuum coater, and spray to form a coating thickness inthe range of 0.1 mils to 3.0 mils, preferably 0.2 to 1.0 mils. Thecoating is particularly advantageous for polymeric substrates includingpolyvinyl chloride, either rigid or flexible PVC, polycarbonates as thehard to adhere polymers such as polypropylene and polyethylene, as wellas the thermoplastic vulcanizates, and thermoplastic olefins (TPO).

[0038] Solvents can be added to aid in application if necessary. Afterapplication of the coating to a substrate, polymerization of the coatingis initiated. The polymerization may be initiated by any method or meansknown in the art for initiating radiation-curable materials. At thepresent invention, it is preferred to initiate polymerization of thecoating by exposing the coating to any source of actinic radiation at awavelength within the ultraviolet or visible spectral regions. Suitablesources of radiation include mercury, xenon, carbon arc and tungstenfilament lamps, sunlight, etc. Exposures may be from less than about 0.1second to 10 minutes or more depending upon the amounts of particularpolymerizable materials and photo-initiators being utilized anddepending upon the radiation source and distance from the source. Thecompositions may also be polymerized by exposure to electron beamirradiation in a dosage typically ranging from less than about 1 megaradto 100 megarad or more. The use of thermal energy during or afterexposure to a radiation source will also generally accelerate the curingreaction, and even a moderate increase in temperature may greatlyaccelerate cure rate.

[0039] An UV curable coating of the present invention can be used inessentially any type of coating or adhesive application known in theart. In particular, though not exclusively, the UV curable coating isparticularly suitable for golf ball application, wherein the golf ballcomprises an ionomer resin layer.

[0040] Typical golf ball cover materials and compositions includethermoplastic ionomer resins such as those sold under the trademarksSURLYN®, available from E.I. Du Pont de Nemours and Co., Wilmington,Del.; or IOTEK®, available from Exxon Chemical Co., Polymers Group,Baytown, Tex.

[0041] The UV curable coating in the invention has enhanced adhesion tothe ionomer substrates, such as SURLYN® resin. Adhesion was tested byusing Cross-hatch test method. Adhesion of an UV coating withoutpolyaziridine varied from 4% to 97% depending on the surface treatment.Adhesion was improved to 100% after polyaziridine incorporated.

[0042] The following examples are provided for purposes of illustratingthe invention and should not be construed in any manner to limit thescope of the invention, which is defined by the claims.

EXAMPLE 1

[0043] A urethane acrylate oligomer is prepared as follows:

[0044] 1103 grams of Desmodur® W (commercially available from Bayer) and0.8 grams of toluhydroquinone are added into a reaction kettle. Thecontents of the reaction kettle are heated to 50° C. under dry air, and724.2 grams of Tone® M-100 (commercially available from Union Carbide)and 2 drops of tin catalyst are then added. The reaction kettle isheated to 50-60° C. for 30 minutes, and then another 724.2 grams ofTone® M-100 and 2 drops of T-9 catalyst are added into the reactionkettle to form a mixture. The mixture is heated at 60-70° C. for about 8hours until NCO<0.25.

EXAMPLE 2

[0045] 45 g urethane acrylate oligomer as in Example 1, 49.7 g acrylicmonomers (a mixture of SR238, SR492 and SR256, which are commerciallyavailable from Sartomer, Inc.), 0.1 g surfactant, and 1.5 g1-hydroxycyclohexyl phenyl ketone (available from Ciba under thetradename Irgacure® 184), 3 g benzophenone, and 0.2 g fluorescentwhitener (available from Ciba under the tradename Uvitex® OB) were mixeduntil homogeneous. To this mixture was added 0.5 g polyaziridine. Thesolution was mixed for another 15 minutes to afford a coating. Thecoating was then sprayed onto a golf ball using HVLP spray techniques(High Volume Low Pressure). The golf ball was then cured under a Fusion®UV lamp system. The total cure energy used was 600 mj/cm² cm² in an airatmosphere. The coating exhibited a high whiteness index and very goodadhesion on the golf ball surface. The golf balls were tested in acannon tester for 50 hits, and no micro cracking or loss of adhesion wasobserved.

EXAMPLE 3

[0046] Formulations were prepared and cured as in Example 2. Aconventional adhesion promoter was added to enhance the adhesion of thecoating to the SURLYN® cover. This was ineffective. In 3-B, 3-C, and3-D, a low level of polyaziridine adhesion promoter was incorporatedinto the formulation. The incorporation of polyaziridine into theformulation improved the adhesion of UV coating from 5% to 100%. TABLE I3-A 3-B 3-C 3-D Urethane oligomer 50 g 50 g 50 g 50 g Acrylate monomers40.5 g 40.4 g 40.2 g 40 g Adhesion promoter THF acrylate 5 g 5 g 5 g 5 gPolyaziridine 0 g 0.1 g 0.3 g 0.5 g Photoinitiators 4.5 g 4.5 g 4.5 g4.5 g Adhesion* 5% 100% 100% 100%

EXAMPLE 4

[0047] Formulations based on Example 2 were prepared with varied levelsof benzophenone. The coatings were applied onto flat plaques of SURLYN®cover and cured as in Example 2. As can be seen from the data in theTable II below increasing the level of benzophenone will increase thewhiteness index of the coating. TABLE II Benzophenone Coating (% byweight) Whiteness index* 2-A 3% 118.28 2-B 2% 114.89 2-C 0 110.50

What is claimed is:
 1. A high solids, low-solvent containing outercoating for a golf ball, comprising a UV curable coating which contains(a) at least one UV-reactive component, (b) a polyfunctional aziridinehaving the formula R—[X—N(CH₂)₂]_(m) in which R is an organic aliphaticradical or a hydrogen atom, X is an alkylene group which may contain anester group, an ether group, an amide group or a similar inert group,and m is a number of 2 to 4, and (c) a photo-initiator.
 2. The coatingof claim 1 wherein said UV-reactive component comprises a urethaneacrylate oligomer (a) formed by reacting diisocyanate with a hydroxylgroup containing acrylate or methacrylate and the product furtherreacted with polyol or (b) reacting a hydroxyl group containing acrylateor methacrylate with a lactone and reacting the product with anisocyanate.
 3. A golf ball comprising a top coat covering formed from aUV-curable coating comprising at least one UV curable acrylate oligomer,a polyfunctional aziridine, and a photoinitiator.
 4. A coated substratecomprising a polymer as substrate and coated with a UV cured coatingcomprising (a) at least one UV-reactive component, (b) a polyfunctionalaziridine having the formula R—[X—N(CH₂)₂]_(m) in which R is an organicaliphatic radical or a hydrogen atom, X is an alkylene group which maycontain an ester group, an ether group, an amide group or a similarinert group, and m is a number of 2 to 4, and (c) a photo-initiator. 5.The coated substrate of claim 3 wherein said UV-reactive componentcomprises a urethane acrylate oligomer (a) formed by reactingdiisocyanate with a hydroxyl group containing acrylate or methacrylateand the product further reacted with polyol or (b) reacting a hydroxylgroup containing acrylate or methacrylate with a lactone and reactingthe product with an isocyanate.
 6. The golf ball according to claim 1wherein UV curable acrylate oligomer has a viscosity within the range of8,000 centipoise to about 40,000 centipoise.
 7. The golf ball accordingto claim 1 wherein the photoinitiator is present in an amount of from 1to 8 % by weight of the coating.
 8. The golf ball according to claim 1wherein the photoinitiator is selected from the group consisting of abenzophenone, benzoin, acetophenone, benzoin methyl ether, Michler'sketone, benzoin butyl ether, xanthone, thioxanthone, propiophenone,fluorenone, carbozole, diethyoxyacetophenone, 2-, 3- and 4-methylacetophenones, 2-, 3-and 4- methoxyacetophenones, 2- and3-chloroxanthones, 2-, and 3-chlorothioxanthones,2-acetyl-4-methylphenyl acetate, 2,2′-dimethyoxy-2-phenyl acetophenone,benzaldehyde, fluorene, anthraquinone, triphenylamine, 3- and4-allyl-acetophenone, p-diacetylbenzene, 3-chloro-2-nonylxanthone,2-chlorobenzophenone, 4-methoxybenzophenone,2,2′,4,4′-tetrachlorobenzophenone, 2-chloro-4′-methylbenzophenone,4-chloro-4′-methylbenzophenone, 3-methylbenzophenone,4-tert-butyl-benzophenone, isobutyl ether, benzoic acetate, benzil,benzilic acid, amino benzoate, methylene blue, 2,2-diethoxyacetophenone,9,10-phenanthrenequinone, 2-methyl anthraquinone, 2-ethyl anthraquinone,1-tert-butyl-anthraquinone, 1,4-naphthoquinone, isopropylthioxanthone,2-chlorothioxanthone, 2-iso-propylthioxanthone, 2methylthioxanthone,2-decylthioxanthone, 2-dodecyl-thioxanthone, 2-methyl-1-[4-(methylthio)phenyl)]-2-morpholinopropanone-1, and any combination thereof.
 9. Agolf ball comprising a top coat covering substantially the entire golfball, the top coat formed from a UV-curable coating comprising 30 to 80%by weight on weight of the coating, of at least one UV reactivecomponent, 10 to 60% by weight of a reactive diluent, a polyfunctionalaziridine in an amount ranging from 0.1 to 15% by weight of theUV-curable coating, and a photoinitiator in an amount ranging from 0.5to 15% by weight of the UV-curable coating.
 10. The coated substrateaccording to claim 3 wherein the UV reactive component is an oligomerselected from the group consisting of urethane acrylate, epoxy acrylateor polyether acrylate, the polyfunctional aziridine is present in thecoating in an amount of from 0.5% to 8% per weight of the coating, andthe photoinitiator in an amount of approximately 1 part per weight ofthe UV-curable coating.
 11. The golf ball according to claim 6 whereinthe UV reactive component comprises a urethane acrylate oligomer at from40% to 70% by weight of the coating and a reactive diluent in an amountof from 10 to 60 % by weight.